Ground testing is often misconstrued by electrical engineers and service technicians who do not perform such testing frequently and routinely. It seems that there are a lot of questions and doubts on evaluating the ground. This technical short article, based upon MeterTester blog, will try to address the twelve most common doubts connected to utilizing ground tester, connections, screening approaches, and safety.
Ok, let's see these doubts and questions. Please note that there are probably tens of other possible issues and unpredictabilities that might popup throughout the ground screening procedure, but we will focus on the most common ones.
Can I use an insulation tester to do the exact same test?
No. This is a common mistake. Field operators are typically issued a Megger instrument from stores, without its being checked to figure out whether it's an insulation or ground tester.
Insulation testers are created to measure at the opposite end of the resistance spectrum from a ground tester.
No one wants premises that step in megohms. Insulation testers utilize high test voltages in the kilovolt range. Ground testers are restricted, for operator security, to low voltages. Insulation testers do frequently have low-voltage, low-resistance connection functions and these are frequently misused to make jiffy ground tests.
Nevertheless, a continuity test can only make an approximate measurement between a set up electrode and a referral ground, which is presumed to have minimal resistance. This does not manage a trustworthy measurement of the resistance the earth offers to a ground fault existing.
Even this arbitrary measurement may not be reputable, given that a dc continuity test can be influenced by soil transients, the electrical sound that is produced by energy ground currents attempting to get back to the transformer, along with other sources.
The required measurement is of resistance; why can't I use a multimeter?
For the exact same reasons that a connection variety on an insulation tester must not be used. Measurements made with a DC multimeter go through distortion by electrical sound in the soil.
A multimeter deals no methods of validating that the resistance showed represents anything other than an approximate measurement in between two hassle-free points.
With a multimeter, one can measure the resistance of the soil in between a ground electrode and some referral point, such as the pipes system, however a fault current may come across a greater resistance.
What is the difference between a two-point, three-point, and four-point test?
Actually, the difference is really the variety of points of contact with the soil. More particularly, these commonly used terms refer to dead earth, fall of capacity, and Wenner technique tests, respectively. In the dead earth technique, contact is made at simply two points: the ground electrode under test and a practical reference ground, such as the pipes system or a metal fence post.
In the fall of potential technique, a real ground tester makes contact by means of the test electrode, plus the present and potential probes. With the Wenner approach, no ground electrode is involved, however rather the independent electrical residential or commercial properties of the soil itself can be measured using a four-probe setup and an acknowledged guideline.